For those who thought the last Bruce Willis movie was a little light on the casualty list, “Olympus Has Fallen” arrives toting the biggest body count since “Die Hard II.”

Bystanders and tourists, soldiers, cops and Secret Service agents fall by the score in a movie about the unthinkable — a terrorist ground assault on Washington, D.C. (Hollywood is providing two such “unthinkable” assaults this year, with “White House Down” due out this summer.)

This is “Die Hard in the White House,” with Gerard Butler manfully manning up as Mike Banning, the lone Secret Service agent survivor after terrorists take over the White House and seize the president and most of the cabinet.

Not without a fight, of course. This president (Aaron Eckhart) boxes. And wait’ll you see the presidential head-butt.

Banning is a former White House detail member, on the outs because of a life-or-death decision he made months before. When the gunship sweeps over D.C., when ordinary Asian tourists turn out to be terrorists, when innocent garbage trucks turn into tanks, Mike’s the man of the moment — dashing back inside his old stamping grounds, where a mastermind (Rick Yune of “Die Another Day” and “The Man With the Iron Fists”) tells the chairman of the Joint Chiefs (Robert Forster) and speaker of the House (Morgan Freeman), “I am the man in control of your White House.”

Banning is the only guy who can get to the fortified bunker where the hostages are. He proceeds to stab, shoot and strangle his way through legions of terrorists, quipping in his updates as he shows off his trophies, by phone, to the rest of the government, which can only ask “Is he alive?” about Mike’s latest catch.

Butler is fine in this part, which demands little more of him than an ability to change magazines like he’s done it before. Many times. Mike has skills, which works against this “Die Hard.” This isn’t John McClane, ordinary cop in over his head. Mike Banning has “special forces” on his résumé, which robs the picture of some of its suspense.

But there’s pathos here, amid the carnage. A good cast (Melissa Leo is a feisty secretary of defense) does what it can with a tin-eared script, making us care who lives and who dies. As an interesting side story, Mike’s wife (Radha Mitchell) is a nurse who deals with the carnage of America’s darkest day in an overwhelmed hospital emergency room.

Better thrillers make more of the whole shaky state of command in such calamities, wavering over terrorist demands, stringing out the suspense and playing up the clock ticking down toward whatever nuclear doomsday awaits should our hero fail. Director Antoine Fuqua (“Shooter”) is plainly dealing with a script that shortchanges all that, and he’s not good enough to overcome it.